1. Field of the Invention
The present invention relates to a recording signal control apparatus capable of optimizing recording conditions or a magnetic recording medium, wherein when controlling signal recording conditions for recording on a particular magnetic recording medium in a magnetic recording and reproduction apparatus, the characteristics of video signal recording and processing circuitry are controlled in such a manner as to match the performance of the magnetic recording medium.
2. Description of Related Art
Usually, in home video tape recorders (hereinafter called VTRs), recording current adjusting means is provided that controls the recording current fed to the recording head coils at an optimum value in order to obtain the maximum playback voltage, as described in "Nyuumon VTR (Introduction to VTR)" by Kotaro Yokokawa, Tokyo Electrical Engineering University Press, pp. 75-78. The recording current value necessary to obtain the maximum playback voltage, i.e., the optimum recording current value, is hereinafter abbreviated as O.R.C.
However, the O.R.C. value varies due to variations in the magnetic tape and head characteristics from one VTR to another. Furthermore, even in the same VTR, the O.R.C. value changes depending on the magnetic tape used, i.e., on the magnetic recording medium used. The O.R.C. value also varies as the characteristics of the magnetic tape arid head vary with time. Moreover, depending on the characteristics of the magnetic tape used, the O.R.C. value varies with frequencies of recorded signals.
In a previously practiced method of setting the recording current characteristic, an average O.R.C. value is obtained by considering the various factors for the above variations as much as possible, and the thus obtained average O.R.C. value is applied indiscriminately for volume-produced VTRs. To overcome such a problem with the prior art, Japanese Patent Application Laid-Open No. 2-187902 (1990) discloses a recording current control apparatus such as shown in FIG. 1.
In FIG. 1, the reference numeral 59 designates a recording head for recording a signal for the detection of O.R.C., 9 represents a magnetic tape, and 60 and 65 indicate rotary transformers. Further, the numeral 61 denotes a recording amplifier, while 62 designates a gain switching controller for controlling the switching of the gain of the recording amplifier 6. The numeral 64 is a playback head For playing back signals recorded on the magnetic tape and the numeral 66 is a front-end playback amplifier For amplifying the playback signal played back by the playback lead 64 and input via the rotary transformer 65. The numeral 67 is a detector for smoothing the playback signal amplified by the front-end playback amplifier 66, and converting it to a d.c. voltage. The numeral 63 is a comparison/decision unit for comparing the magnitudes of multiple d.c. voltages output from the detector 67 and, based on the result of the comparison, issuing an instruction to the gain switching controller 62 fop gain setting. The gain switching controller 62 controls the gain of the recording amplifier 61 in accordance with the gain setting instruction given from the comparison/decision unit 63.
FIG. 2 is a characteristic diagram showing an example of a playback head output frequency (f) characteristic for each of tapes A and B having different characteristics. FIG. 3 is a characteristic diagram showing an example of a reproduced video signal frequency characteristic for each of the tapes A and B when video signals are recorded and played back using the tapes, A and B, having the video head output frequency characteristics shown in FIG. 2.
The operation of the above control apparatus will now be described. In recording, signals input to the recording amplifier 61 are amplified by the recording amplifier 61 and applied via the rotary transformer 60 to the recording head 59 for recording on the magnetic tape 9. Recording is performed with a plurality of recording currents of different values based on the instructions given from the gain switching controller 62. In playback, the signals recorded on the magnetic tape 9 are played back by the playback head 64 and supplied via the rotary transformer 65 to the front-end amplifier 66 for amplification. The playback signals amplified by the front-end amplifier 66 are fed to the detector 67 where the signals are smoothed. The plurality of signals smoothed by the detector 67 are input to the comparison/decision unit 63 where the magnitudes of the plurality of input signal voltages are compared to determine the O.R.C. value.
Conventional VTRs are designed to the lowest grade of magnetic tape to prevent magnetic reversion (which leads to recording errors) and secure a sufficient signal-to-noise ratio for any grade of magnetic tape. As a result, when a high-grade magnetic tape is used, the recorded picture is only excellent in the signal-to-noise ratio although such a tape could record finer details without degrading the signal-to-noise ratio.
Furthermore, with the recording current control apparatus of FIG. 1 having the configuration described above, the O.R.C. value can be accurately measured for each individual magnetic tape, but since the O.R.C. value is measured at a single predetermined frequency, no correction is made for the frequency characteristic of the magnetic tape. The sideband recording and reproduction levels of the frequency-modulated wave of the recorded and reproduced video signal vary depending on the characteristics of the various magnetic tapes, as shown in FIG. 2, causing such problems as variations in picture quality when the video signal is reproduced, as can be seen from the reproduced video frequency characteristics shown in FIG. 3.
Moreover, since the recording current control apparatus of the above configuration does not have means for storing magnetic tape characteristics measured, it is necessary to make the measurement over again even when using a magnetic tape of the same grade.